This invention relates to monitoring equipment for processing of liquids used in products for human consumption, e.g., dairy products such as milk, cream, and ice cream mix, other liquid food products, e.g., fruit juices and soups, or pharmaceuticals. The invention is more particularly concerned with an adapter and a technique for employing a standard pressure gauge on sanitary conduits in which such liquid products are processed, and which permits the pressure gauge to be changed out or replaced when necessary, without incurring high material or labor costs and while maintaining sanitary conditions within the conduit. The invention is more specifically directed to a pressure gauge adapter which employs diaphragms and a piston to transmit the pressure of the process liquid to a working liquid which in turn transmits the process liquid pressure to the pressure gauge.
Pasteurization is a process for heat treating milk or other food or ingestible product in order to kill pathogens such as bacteria or other microorganisms. The U.S. Public Health Service has published standards for equipment for the pasteurization of milk and other milk products, and there are similar regulations concerning equipment for processing other products. By law, the milk or other product has to be heated to certain temperatures and held at a particular temperature. The pressures and pressure differentials of the product have to be closely monitored at certain points in the process. This means that working pressure gauges have to be present in the conduit, and must be replaced whenever they fail. On the other hand, in order to ensure that the sanitary conduit can be cleansed and sanitized between processes, the conduit is designed so that it can be completely cleaned of any milk or other product by washing it and rinsing it with a cleaning fluid that must reach every point on the interior of the conduit. No threaded connectors can be used anywhere that the liquid product flows, because of the difficulty in cleaning the threads.
Standard pressure gauges typically have a threaded stem that is used for securing the gauge into a threaded nipple in the associated equipment. However, there cannot legally be any threaded connections at any point at which the product would come into contact with the threads. Because these standard gauges rely on threaded connections to install them and hold them in place, an alternative technique has been employed for using pressure gauges and the like in sanitary conduits.
One technique that has been employed previously has been to install a diaphragm and flange disk onto the pressure gauge, and then to clamp the disk and diaphragm in place on top of an annular flange portion of a stub member that is affixed onto the conduit. A sanitary clamp, e.g., a so-called tri-clamp, compresses a sealing gland or ring between these two flanges, so there are no threads exposed to the product in the sanitary conduit. Unfortunately, these specially constructed gauges are many times more costly than the standard pressure gauges, and thus much more expensive to replace.
In addition, the standard pressure gauge and the diaphragm type gauge mentioned above do not have any means for disclosing a leak or a failure of a seal within the gauge assembly.
In a regenerative heat exchanger of the type that is used in many pasteurizers, critical temperature differences have to be maintained between the raw product side and the pasteurized product side (typically, only a few degrees). To achieve this, flow rates must be kept within narrow limits, which requires critical pressure differentials. For efficient operation it is important to monitor pressure there very closely. It is also desirable to be able to replace a gauge quickly when it fails, and to employ standard gauges of relatively low cost, yet still of acceptable accuracy.